The main function of Facebook is to spy on people, the providers of the data. All data gathered is then sold to paying customers. They make all their money this way.
If they only had a graph with persons and relations between these persons and did nothing else with it than show this to these people, maybe we were not facing this discussion now.
The cynic in me would say: store all data on EU soil ;)
you can look at the 30% in two ways:
1/ the dev is paying
2/ the user is paying
I look at it from 2/ so Apple charges me 30 on top of 70 which is almost 43% extra for consuming a service via their distribution channel, for which I already paid a premium price.